1. Field of the Invention
The present invention relates to a fuel supply pump in a system for injecting pressurized fuel to an internal combustion engine such as a diesel engine.
2. Description of the Related Art
For controlling the quantity of fuel discharged from a fuel injector with high precision so as to most efficiently run an engine, it is advantageous to use electrical control means to open and close the fuel injector. For electrical controlling, it is preferable that the object under control be as simple as possible. Accordingly, a conventional electronically controlled fuel injecting system is constructed in such a manner that the fuel injector is supplied with highly pressurized fuel and a valve provided in the injector is simply opened or closed by the electrical control means.
Thus, in the conventional system, a pressure regulator is provided to adjust the pressure of the fuel to a predetermined value. Usually, a relief mechanism is provided in the pressure regulator to relieve residual fuel so that the pressure regulator obtains and maintains a constant pressure value.
In a system including a relief mechanism, however, there is a problem in that air bubbles are caused in the fuel due to the rise of fuel temperature caused by friction of the fuel during relief thereof. Further, power loss of the pump is caused because the pump must be able to discharge the relieved fuel as well.